Field access magnetic bubble memory device

ABSTRACT

A field access magnetic bubble memory device including a memory chip applied with an in-plane magnetic field at need is disclosed. At a transient stop operation of the device before its interrupted state, an in-plane field is removed after it has been held for a predetermined period following the cessation of rotation thereof. The in-plane field may be increased upon the cessation of rotation thereof. At a transient start operation of the device after the interrupted state, an in-plane field having no rotation and the same direction as at the transient stop operation is applied for a predetermined period before the initiation of rotation thereof. The applied in-plane field may be increased upon the initiation of rotation thereof.

LIST OF PRIOR ART REFERENCES (37CFR 1.56(a))

The following references are cited to show the state of the art:

(1) Japanese Patent Application Laid-Open No. 88438/74, Hiroshima andYoshizawa, Aug. 3, 1974

(2) I. S. Gergis, T. T. Chen and L. R. Tocci "The effect of dc in planefield on the operation of field access bubble memory devices," IEEETrans on Magnetics, Vol. MAG-12, No. 1, pp 7 ˜ 14, January 1976

(3) Maekawa, Komatsu and Takai, "The investigation on the driving ofrotating magnetic field for magnetic bubbles," the research materials bythe Japanese joint research committee for electronic devices andmagnetic materials, March 1974

The present invention relates to a field access magnetic bubble memorydevice using an in-plane rotating magnetic field and more particularlyto transient stop and start operations of such a device before and afterits interrupted state.

The "transient stop operation" of the device referred to in thespecification includes at least a period from the cessation of rotationof an in-plane magnetic field to the removal of the in-plane fieldbefore the interrupted state of the device. The "transient startoperation" of the device includes at least a period from the applicationof an in-plane magnetic field to the initiation of rotation of thein-plane field after the interrupted state of the device.

A conventional field access magnetic bubble memory device using anin-plane rotating magnetic field comprises a memory chip including alayer of magnetic material provided on a non-magnetic substrate andmagnetic bubble transfer paths formed on the magnetic material layer. Atypical example of the magnetic bubble transfer paths is a T-bar patternof magnetically soft material such as permalloy which includesalternating bar and T-shaped segments. Instead of the T-bar pattern maybe used a well known suitable pattern such as so-called Y-bar, Y--Y orchevron pattern. The memory chip is surrounded by a drive coil assemblywhich usually includes X- and Y-direction drive coils for generating anin-plane rotating magnetic field. The drive coil assembly is encompassedby a magnet assembly for generating a biasing magnetic field which isperpendicular to the magnetic material layer of the memory chip andforms stabilized magnetic bubbles in the magnetic material layer.

The operation of the magnetic bubble memory may be interrupted at need.In that case, the contents stored before the interruption must bereserverd throughout the transient stop and start operations. The memoryhaving such a property is called a non-volatile memory. The JapanesePat. Application No. 129399/72 laid open on Aug. 3, 1974 under theJapanese Patent Application Laid-Open No. 88438/74 discloses aconventional technique for achieving this purpose in the case where thecombination of X- and Y-direction magnetic field components H_(X) andH_(Y) of sinusoidal waveforms shifted in phase from each other by 90° isused as an in-plane rotating magnetic field. According to the disclosedtechnique, a transient stop operation before an interrupted state iscarried out in such a manner that one of the H_(X) and H_(Y) components,for example, the H_(Y) component is removed for the cessation ofrotation of the in-plane field when the H_(Y) component has reached itsmagnitude of zero and the H_(X) component is removed when the H_(X)component has reached its magnitude of zero after the lapse of the 1/4cycle of the normal operation of the device following the cessation ofrotation of the in-plane field. At a transient start operation after theinterrupted state, the component H_(X) having the same direction as atthe transient stop operation is applied and the component H_(Y) havingits direction opposite to that just before the cessation of rotation ofthe in-plane field is applied for the initiation of rotation of thein-plane field after the lapse of the 1/4 cycle of the normal operationof the device following the application of the H_(X) component. However,there is a problem that the margin of a biasing magnetic field in suchtransient stop and start operations is smaller than that in the normaloperation, i.e. during the continuous rotation of the in-plane field.

The above-described Japanese Patent Application Laid-Open No. 88438/74also discloses methods for preventing the decrease in the margin of abiasing field at the transient stop/start operation. According to one ofthe disclosed methods, the in-plane field or one of the H_(X) and H_(Y)component is held during the transient stop operation and even duringthe interrupted state of the device as it was upon the cessation ofrotation of the in-plane field. At the transient start operation, theheld in-plane field is directly rotated. In this method, however,current must be flown through the drive coil even during the interruptedstate. According to the disclosed other method, the transient startoperation is carried out in such a manner that the applied in-planefield is slowly increased and thereafter rotated. However, this methodtakes too long access time.

An object of the present invention is to provide a field access magneticbubble memory device in which the margin of a biasing magnetic field atthe transient stop/start operation is improved without imposing anysevere restriction on the tolerances of a memory chip and a drivecircuit.

The present invention is directed to a field access magnetic bubblememory device comprising a memory chip and an in-plane magnetic fieldgenerating means for generating in the memory chip an in-plane magneticfield which cyclically rotates during normal operations of the deviceand is held without rotating and with the same direction duringtransient stop and start operations of the device before and after aninterrupted state of the device between the normal operations. Accordingto the present invention, the in-plane field at the transient stopoperation has its magnitude which gradually decreases over a periodexceeding the 1/4 cycle of the normal operation, its magnitude which isconstant for a predetermined period, or its magnitude which is largerthan that at the normal operation.

Now, the present invention will be explained in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates a conventional stop/start operation using twomagnetic field components H_(X) and H_(Y) of sinusoidal waveformsshifted in phase from each other by 90°;

FIG. 2 shows the locus of the vector of an in-plane rotating magneticfield generated by the combination of the two field components H_(X) andH_(Y) in FIG. 1;

FIG. 3 shows the relationship between the coordinate of the rotatingfield vector and the memory chip arrangement;

FIG. 4 illustrates a conventional stop/start operation using two fieldcomponents H_(X) and H_(Y) of triangular waveforms shifted in phase fromeach other by 90°;

FIG. 5 shows the locus of the vector of an in-plane rotating fieldgenerated by the combination of the two field component H_(X) and H_(Y)in FIG. 4;

FIG. 6 illustrates a stop/start operation in which the in-plane field isheld during a period from the cessation of rotation thereof to theinitiation of rotation thereof;

FIG. 7 illustrates a conventional stop/start operation in which thein-plane field is slowly applied;

FIG. 8 illustrates a stop/start operation in which the in-plane field isslowly decreased to zero after the cessation of rotation thereof;

FIG. 9 illustrates the same stop/start operation as shown in FIG. 8,except the use of two magnetic field components of triangular waveforms;

FIGS. 10A and 10B illustrate stop/start operations in which a holdingfield having its magnitude equal to the peak value H_(r) of the in-planefield at the continuous rotating operation is applied for apredetermined period;

FIGS. 11A and 11B illustrate the same stop/start operations as shown inFIGS. 10A and 10B, except that the holding field H_(h) has its magnitudesmaller than H_(r) ;

FIGS. 12A and 12B illustrate the same stop/start operations as shown inFIGS. 10A and 10B, except that the holding field is slowly removed;

FIGS. 13A and 13B illustrate the same stop/start operations as shown inFIGS. 11A and 11B, except that the holding filed is slowly removed;

FIGS. 14A and 14B illustrate stop/start operations in which a magnitudeof the in-plane field is increased only upon the cessation of rotationthereof;

FIGS. 15A to 15H illustrate stop/start operations in which a magnitudeof the in-plane field is increased only upon the cessation of rotationthereof and a holding field is thereafter applied for a predeterminedperiod;

FIGS. 16A and 16B illustrate stop/start operations in which a magnitudeof the in-plane field is increased at the phase 90° before the instantof the cessation of rotation thereof;

FIGS. 17A to 17H illustrate stop/start operations obtained through thecombinations of the operations in FIGS. 16A and 16B with those in FIGS.8 to 13A and 13B;

FIGS. 18A and 18B illustrate stop/start operations in the case where thesinusoidal magnetic field undershoots;

FIGS. 19A to 19D illustrate stop/start operations in which the in-planefield applied at the start operation has its magnitude larger than thatat the normal operation;

FIGS. 20A and 20B show circuits of a first embodiment of the presentinvention;

FIG. 21 shows waveforms appearing at various points in the circuitsshown in FIGS. 20A and 20B;

FIG. 22 shows in graphic representation the characteristics of thecircuits in FIGS. 20A and 20B;

FIG. 23 shows in side view a module in which a memory chip is inclinedto yoke plates;

FIG. 24 shows a circuit of a second embodiment of the present invention;

FIG. 25 shows waveforms useful in explaining the operation of thecircuit shown in FIG. 24;

FIG. 26 shows a circuit of a third embodiment of the present invention;

FIG. 27 shows waveforms useful in explaining the operation of thecircuit shown in FIG. 26;

FIG. 28 shows in graphic representation the characteristic of thecircuit in FIG. 26;

FIG. 29 shows a circuit of a fourth embodiment of the present invention;

FIG. 30 shows waveforms useful in explaining the operation of thecircuit in FIG. 29;

FIG. 31 illustrates a rotating magnetic field whose vector describes apseudo-asteroid curve;

FIG. 32 shows a circuit for supplying the signal φ₃ used in the circuitof FIG. 24; and

FIG. 33 shows waveforms of input and output signals in the circuit ofFIG. 32.

Prior to the description of the embodiments of the present invention,the conventional methods and the associated problems will be explainedwith the aid of FIGS. 1 to 7.

The conventional stop/start operation has been performed in the manneras shown in FIG. 1 or 4. FIG. 1 showing the case where two sinusoidallyvarying magnetic field components H_(X) and H_(Y) shifted in phase fromeach other by 90°, is disclosed the Japanese Pat. application Laid-OpenNo. 88438/74. In this case, H_(Y) vanishes at the time t₁ and is kept atzero from that time instant forward so that the rotation of the in-planemagnetic field having rotated counterclockwise before the time t₁ asshown in FIG. 2 is ceased at the time t₁, pointing to the negativedirection of H_(X). After the 1/4 cycle of the normal operation, H_(X)vanishes at the time t₂ and is kept at zero thereafter. The in-planefield kept still pointing to the negative direction of H_(X) graduallydecreases in its vector norm until it vanishes completely at the time t₂as shown in FIG. 2. For the transient start operation, H_(X) starts atthe time t₃ varying sinusoidally in the negative direction and reachesits maximum magnitude at the time t₄ when H_(Y) also starts varyingsinusoidally in the positive direction. As a result, the in-plane fieldrotates counterclockwise after the time t₄.

Thus, the direction of the in-plane field applied at the transient startoperation must be identical to that of the in-plane magnetic field fromits rotation cessation to its removal at the transient stop operation.There exists a certain relationship between that field direction and thememory chip arrangement, i.e. the directions of the T-bar patterns inthe chip, and FIG. 3 shows an example thereof. In FIG. 3, referencenumerals 5 and 6 respectively indicate bonding pads and a T-bar patternof minor loops.

FIG. 4 shows the case where magnetic field components for forming anin-plane rotating magnetic field have triangular waveforms. The vectorof the in-plane rotating magnetic field in this case describes a locusof square as shown in FIG. 5.

However, detailed experiments have revealed that the margin of a biasingmagnetic field at the stop/start operation is smaller than at the normaloperation, i.e. during the continuous rotation of the in-plane field andalso that if a constant in-plane magnetic field having a small magnitudeis applied with its direction opposite to that of the in-plane fieldupon the cessation of rotation thereof, the bias field margin isconsiderably decreased. In connection therewith, one can refer to I. S.Gergis, T. T. Chen and L. R. Tocci "The effect of dc in-plane field onthe operation of field access bubble memory devices", IEEE Trans onMagnetics, Vol. MAG-12, No. 1, pp 7 ˜ 14, Jan. 1976.

In order to prevent the decrease in the bias field margin at thestop/start operation, the abovedescribed Japanese Pat. applicationLaid-Open No. 88438/74 shows a method in which the in-plane field isheld present during the transient stop operation and even during theinterrupted state of the device and the held in-plane field is directlyrotated at the transient start operation, as shown in FIG. 6. Thismethod, however, requires current to flow through the drive coil evenduring the interrupted state of the device, i.e. during the period inwhich the rotation of the in-plane field is ceased. The Japanese Pat.application Laid-Open No. 88438/74 also shows a method in which thein-plane field applied at the transient start operation is slowlyincreased to the rated level assumed at the continuous rotatingoperation and thereafter caused to initiate the rotation thereof, asshown in FIG. 7. This method, however, has a drawback that an accesstime is too long since the in-plane field in only gradually increasedafter the demand for memory reference.

The present inventors have revealed the facts listed in the followingitems (1) to (10) as a result of repeated experiments of fabricating andmeasuring memory chips.

(1)--The difference between the bias field margins at the normaloperation and the stop/start operation can be eliminated or decreased ifa constant in-plane field is always applied in the direction identicalto that of the in-plane rotating field upon the cessation of rotationthereof. However, if the constant in-plane field has too greatmagnitude, the bias field margin at the normal operation is lowered.

(2)--If the in-plane field is slowly decreased only during the transientstop operation as shown in FIG. 8 or 9 instead of the method shown inFIG. 7, the decrease in the bias field margin can be prevented. In thatcase, the transient start operation may employ the manner shown in FIG.1 or 4. Thus, an access time can be shortened. In this method, it isnecessary that a period over which the in-plane field graduallydecreases should exceed the 1/4 cycle of the normal operation.

(3)--As regards a method of reducing the in-plane field to zero, thein-plane field may be removed after a constant in-plane field H_(r)having its magnitude equal to that of the in-plane field at the normaloperation or a constant in-plane field H_(h) having its magnitudesmaller than that of the in-plane field at the normal operation has beenheld for a predetermined period, as shown in FIGS. 10A, 10B, 11A or 11B.

(4)--If the in-plane field is rapidly decreased, the bias field marginsin some chips are decreased. The decrease in the margins in those chipscan be prevented by resorting to the manners shown in FIGS. 12A, 12B,13A or 13B.

(5)--If some chips cannot be free from the decrease in the bias fieldmargin even according to the methods described in the above items (2) to(4), the decrease in the margin in such chips can be prevented by makingthe magnitude of the in-plane magnetic field upon the cessation ofrotation thereof larger than that at the normal operation, as shown inFIG. 14A or 14B.

(6)--The bias field margins of some chips which cannot be prevented fromdecreasing even by the method described in the above item (5), can beprevented from decreasing by combining the method in the above item

(5) with the methods in the above items (2) to (4), as shown in FIGS.15A to 15H.

(7)--If in a chip the margin cannot be prevented from decreasing even byresorting to the method described in the above item (6), the decreasecan be eliminated by increasing a magnitude of the in-plane field at thephase 90° before the cessation of rotation thereof, as shown in FIGS.16A and 16B.

(8)--If the method described in the above item (7) has no effect indecreasing the margin, the decrease can be prevented by combining themethod in the above item (7) with the method in the above items (2) to(4), as shown in FIGS. 17A to 17H.

(9)--As shown in FIG. 18A, when the sinusoidal magnetic fields are putoff, the fields are liable to undershoot owing to circuitcharacteristic. The undershooting of H_(Y) at the time t₁ causes littledecrease in the margin since H_(X) is maximum at the time t₁, but theundershooting of H_(X) at the time t₂ decreases the margin to aconsiderable extent since the undershooting forms a field in theopposite direction after the cessation of rotation. However, if aholding magnetic field is applied for a certain period, theundershooting of H_(X) can be prevented from forming a reverse field, asshown in FIG. 18B, so that rather a large undershooting can beequivalently eliminated.

(10)--The decrease in the margin can be prevented by making a magnitudeof the in-plane field at the transient start operation larger than thatat the normal operation, as shown in FIG. 19A, 19B, 19C or 19D. Thismethod may be combined any one of the abovedescribed methods.

As described above, the present invention, which has been made on thebasis of the above facts obtained as a result of repeated experiments,aims at providing a field access magnetic bubble memory device havinglarge allowances for chip and circuit and a short access time.

Now, the present invention will be described by way of embodiments.

EMBODIMENT I

FIGS. 20A and 20B respectively show in-plane magnetic field drivecircuits for the X- and Y-directions, which perform in combination theoperation as shown in FIG. 8. FIG. 21 shows waveforms useful inexplaining the operation.

In FIG. 20A showing the X-direction drive circuit, transistors Q₁ and Q₂are alternately rendered conductive in the normal operation to generateat a point P_(x) a voltage having a rectangular waveform. An X-directiondrive coil L_(x) is connected in series with a resonance capacitor C toform a series resonance circuit which is connected with the point P_(x).Voltage waveforms φ₁ and φ₂ shown in (I-X) of FIG. 21 are applied to thebases of the transistors Q₁ and Q₂, respectively. As seen from (I-X) ofFIG. 21, the transistor Q₂ is turned on for the transient stopoperation. When the current iL_(x) through the coil L_(x) reaches thenegative maximum at the time t₁, a voltage φ₄ is shifted up to be apositive level so that a transistor Q₄ is turned on. Thereafter, thevoltage φ₂ is reduced to zero to turn off the transistor Q₂. Theresonance energy stored in the coil L_(x) continues to be released ascurrent through the transistor Q₄. The current gradually decreases andvanishes at the time t₂ due to resistance loss in circuit, as shown asiL_(x) (Q₄ used) in FIG. 21. The circuit is so designed that t₂ -t₁ mayexceed the 1/4 cycle of the normal operation. For the transient startoperation, the transistor Q₁ is first turned on and then a transistor Q₃is turned on, to cause the capacitor C to be charged so as to develop avoltage of +60V thereacross. Thereafter, the transistor Q₃ is cut offand after Q₄ is cut off, the transistor Q₂ is turned on at the time t₃to start the resonance of the series resonance circuit.

In FIG. 20B showing the Y-direction drive circuit, such transistors asthe transistors Q₃ and Q₄ shown in FIG. 20A are not used. In FIGS. 20Aand 20B, equivalent components are indicated by similar referencecharacters. As shown in FIG. 21 (I-Y), the voltage waveforms φ₁ ' and φ₂' applied to the transistors Q₁ and Q₂ of the Y-direction drive circuitare 90° out of phase from the voltage waveforms φ₁ and φ₂, respectively.

As a result, the dynamic margin characteristics are obtained as shown inFIG. 22, in which the curve 1 corresponds to the normal operation, thecurve 2 to the case where the transistor Q₄ is used, and the curve 3 tothe case where the transistor Q₄ is not used. The case where thetransistor Q₄ is not used, is represented by the signal iL_(x) (Q₄ notused) in FIG. 21 and in this case, the transistor Q₄ is not conducted atthe transient stop operation. In this case, there exists about 5% ofundershooting and the dynamic margin is very narrow as shown in FIG. 22.However, when the transistor Q₄ is operated, the dynamic margin roughlyequal to that at the normal operation can be obtained through the upperlimit at the stop/start operation is smaller by 4 ˜ 5 Oe!.

Incidentally, by inclining the drive coils 18 and 19 with the memorychip 17 mounted therein, at an angle θ of about 2° to yoke plates 15 andby applying a constant in-plane magnetic field (about 3 Oe! in thedirection of the in-plane field upon the cessation of rotation thereof,the fall by 4 ˜ 5 Oe! of the upper limit of the margin at the stop/startoperation can be prevented so that the margin at the stop/startoperation substantially equal to that at the normal operation can beobtained. In FIG. 23, reference numeral 16 indicates a permanent magnet.

EMBODIMENT II

FIG. 24 shows an in-plane magnetic field drive circuit for theX-direction which is suitable to perform such operations as shown inFIGS. 10 to 13. In this embodiment, an in-plane magnetic field drivecircuit for the Y-direction may be the same as that shown in FIG. 20B.

The in-plane field H_(x) in FIG. 1 is applied or removed at the time atwhich the coil current vanishes and the capacitor voltage is maximumwhile the cessation and initiation of rotation of the in-plane fieldtake place respectively at the times t₁ and t₄, as shown in FIG. 1. Atthose time instants, the capacitor voltage is zero and the coil currentis maximum with respect to H_(X). Accordingly, even if the transistorsQ₁ and Q₂ are turned off at the time t₁ and the coil current flowsthrough the transistor Q₃, no transient phenomenon takes place. In likemanner, if the transistor Q₃ is turned on befor the time t₄ and cut offsimultaneously with the start of operations of the transistors Q₁ andQ₂, no transient phenomenon can be observed. FIG. 24 shows a circuit forperforming such an operation as above and FIG. 25 shows waveforms usefulin explaining the operation of the circuit in FIG. 24. The circuit shownin FIG. 24 performs the operations shown in (I) to (IV) of FIG. 25,depending upon the period of conduction of the transistor Q₂ and thewaveform of the voltage applied to the base of the transistor Q₃. (I) to(IV) of FIG. 5 correspond respectively to the operations shown in FIGS.12, 10A, 11A and 13A. The circuit can produce a drive waveform suitableto the stop/start operation, as indicated at iL_(x) in FIG. 25, andenjoy almost the same effect as in FIG. 22. With this circuit, thewaveform of the current during the holding period at the start and stopoperations can be arbitrarily determined. Only the restriction is thatthe current waveform is continuous at the times t₁ and t₄ and has norapid change at those time instants.

In this case, too, the margin of the biasing field is increased byinclining the coils with the chip at an angle to the yoke plates, asshown in FIG. 23.

EMBODIMENT III

FIG. 26 shows a circuit which is a combination of an in-plane fielddrive circuit for the X-direction, for performing the same operation asshown in FIG. 1 and a circuit for causing only pulse current to flowthrough the coil L_(x) of the drive circuit. Thus, in this circuit, thepulse current is superposed on the coil current only during thetransient stop operation. FIG. 27 shows waveforms useful in explainingthe operation of the circuit shown in FIG. 26. The circuit in FIG. 26 isadapted to perform the operations shown in FIGS. 14A, 15A, 15C, 15E and15G and actually performs one of the operations represented by thewaveform diagrams in (I) to (V) of FIG. 27.

As shown in FIG. 27, the transistors Q₁ and Q₂ are alternately turned onat the normal operation and the transistor Q₂ is cut off at the time t₂to reduce the coil current to zero (curve iL_(x) labeled "Q₄ not used").When a signal having a waveform φ₄ is applied to the base of thetransistor Q₄, a current having a waveform iC flows through the coilL_(x) so that a drive current represented by solid curve at iL_(x) isobtained. Just before the transient start operation the transistor Q₃ isturned on and after the polarity of the capacitor C has been inverted,the transistor Q₂ is turned on at the time t₃.

The chip which had been subjected to a performance test, proved to havea bias field margin of about 10 Oe!, as shown by the curve 1 in FIG. 28,but it was not actuated during the start/stop operation in whichtransistor Q₄ is not actuated, the margin being zero. In the case wherethe coils with the chip mounted had no inclination (constant in-planefield H_(in) =O), different from the case shown in FIG. 23, a margin ofabout 5 Oe! was obtained, as shown by the curve 2b in FIG. 28, byactuating the transistor Q₄. When the angle of inclination was about 2°,as in FIG. 23, and when a constant in-plane field of about 3 Oe! wasapplied, the margin represented by the curve 2a in FIG. 28 was obtainedwhich was almost the same as the margins at the normal operation.

In this circuit, by changing the waveform φ₄, the current iC can besuperposed also at the transient start operation (as in the operationsshown in FIGS. 19A and 19B). In another performance test, a margin ofabout 5 Oe!, which corresponds to the curve 2b in FIG. 28, was obtainedwhen the pulse current had been superposed on the coil current at thestop/start operation.

Moreover, in this embodiment, a Y-direction magnetic field drivecircuit, when constructed in the same constitution as in FIG. 26, canclearly perform one of the operations shown in FIGS. 16A, 17A, 17C, 17Eand 17G.

EMBODIMENT IV

FIG. 29 shows another embodiment of the present invention in which theX- and Y-direction magnetic field drive circuits are so designed as togenerate triangular waveforms. In this circuit in FIG. 29, the presentinventinn can be realized only by changing the input signal. Namely, asshown in FIG. 30, if the last half cycle T' is set to be longer than thehalf cycle T/2 during the normal operation such that T'>T/2, then thelast, negative peak of the in-plane field H_(X) can be higher than thatduring the normal operation. A similar effect can be realized also atthe transient start operation as shown in FIG. 28. As a result of theperformance test with this circuit, the same characteristics as thoseshown in FIG. 28 were obtained.

The circuit shown in FIG. 29 can generate a magnetic field vector whichdescribes a pseudoasteroid for a suitably changed input signal (seeMaekawa, Komatsu and Takai, "The investigation on the driving ofrotating magnetic field for magnetic bubbles", the research materials bythe Japanese joint research committee for electronic devices andmagnetic materials, Mar. 1974). Also in this case, the present inventioncan be realized simply by changing the input signal appropriately. Theperformance test with this circuit revealed an excellent result.

The formation of the signal waveforms φ₁, φ₂, φ₃ and φ₄ used in theabove embodiments I to IV is well known. For example, any suitable pulsegenerator circuit which can generate pulses having variable raise andfall times can be used. FIG. 32 shows a circuit for supplying the signalφ₃ used in the circuit of FIG. 24. In FIG. 32, an input signal A havinga predetermined pulse duration time from a suitable pulse generator notshown is applied to the base of a transistor Q₁₁. A resistor R₁₁determines the pulse raise time t_(r) of the output signal B as shown inFIG. 33. The raise time t_(r) proportionally depends upon the resistancevalue of the resistor R₁₁. A resistor R₁₂ determines the pulse fall timet_(f) of the output signal B, which time proportionally depends upon theresistance value of the resistor R₁₂.

It should be understood that the present invention is not limited to thespecified embodiments as described and shown above and any modificationor variation can be made within the teachings of the present invention.Though the in-plane field at the transient stop and/or start operationhas utilized that at the normal operation, an in-plane magnetic fieldfrom another source can be used for the transient stop and/or stopoperation so far as the source provides an in-plane field having itswaveform as has been used in the shown embodiments.

What is claimed is:
 1. In a field access magnetic bubble memory devicecomprising a memory chip and an in-plane magnetic field generating meansfor generating in said memory chip an in-plane magnetic field whichcyclically rotates during normal operations of the device and is heldwithout rotating and with the same direction during transient stop andstart operations of the device before and after an interrupted state ofthe device between said normal operations,the improvement in that thein-plane field generated by said in-plane field generating means at saidtransient stop operation has its magnitude which gradually decreasesover a period exceeding the 1/4 cycle of said normal operation.
 2. Afield access magnetic bubble memory device according to claim 1, whereinsaid device further comprises a means for applying at least at saidtransient stop operation a constant magnetic field in the same directionas the direction of the in-plane field upon the cessation of rotationthereof.
 3. In a field access magnetic bubble memory device comprising amemory chip and an in-plane magnetic field generating means forgenerating in said memory chip an in-plane magnetic field whichcyclically rotates during normal operations of the device and is heldwithout rotating and with the same direction during transient stop andstart operations of the device before and after an interrupted state ofthe device between said normal operations, the in-plane field beingremoved during said interrupted state of the device,the improvement inthat the in-plane field generated by said in-plane field generatingmeans at said transient stop operation has its magnitude which isconstant for a predetermined period prior to removal of said in-planefield during said interrupt state.
 4. A field access magnetic bubblememory device according to claim 3, wherein the magnitude of thein-plane field at said transient stop operation gradually decreases fromsaid constant magnitude.
 5. A field access magnetic bubble memory deviceaccording to claim 3, wherein said constant magnitude of the in-planefield at said transient stop operation is equal to that magnitude of thein-plane field upon the cessation of rotation of the in-plane field. 6.A field access magnetic bubble memory device according to claim 3,wherein said constant magnitude of the in-plane field at said transientstop operation is smaller than that magnitude of the in-plane field uponthe cessation of the in-plane field.
 7. A field access magnetic bubblememory device according to claim 3, wherein the in-plane field at saidtransient start operation has its magnitude which is constant for apredetermined period.
 8. A field access magnetic bubble memory deviceaccording to claim 3, wherein said device further comprises a means forapplying at least at said transient stop operation a constant magneticfield in the same direction as the direction of the in-plane field uponthe cessation of rotation thereof.
 9. In a field access magnetic bubblememory device comprising a memory chip and an in-plane magnetic fieldgenerating means for generating in said memory chip an in-plane magneticfield which cyclically rotates during normal operations of the deviceand is held without rotating and with the same direction duringtransient stop and start operations of the device before and after aninterrupted state of the device between said normal operations,theimprovement in that the in-plane field generated by said in-plane fieldgenerating means at said transient stop operation has its magnitudewhich is larger than that at said normal operation.
 10. A field accessmagnetic bubble memory device according to claim 9, wherein themagnitude of the in-plane field at said transient stop operationgradually decrease from said larger magnitude.
 11. A field accessmagnetic bubble memory device according to claim 9, wherein the in-planefield at said transient stop operation maintains said larger magnitudefor a predetermined period.
 12. A field access magnetic bubble memorydevice according to claim 9, wherein the in-plane field at saidtransient stop operation maintains a magnitude thereof smaller than saidlarger magnitude for a predetermined period.
 13. A field access magneticbubble memory device according to claim 9, wherein the in-plane field atsaid transient start operation has its magnitude which is larger thanthat at said normal operation.
 14. A field access magnetic bubble memorydevice according to claim 9, wherein said device further comprises ameans for applying at least at said transient stop operation a constantmagnetic field in the same direction as the direction of the in-planefield upon the cessation of rotation thereof.